[mberz]

This pull request improves the handling of physical surface groups in the room geometry import process and adds a corresponding test to ensure correctness. It adds support for physical groups that span multiple surfaces.

• Updated the _import_room_geometry method in pyroomacoustics_interface.py to support physical groups (materials) that span multiple surfaces, ensuring all surfaces in a group are processed, not just the first one.
• Added a new test test_import_room_geometry_multi_surface_group in test_pyroomacoustics_backend.py to verify that all surfaces of a physical group are imported as walls, not just the first, and that merging surfaces into a single group maintains the correct wall count.

[Copilot]

🟢 Approval recommended

Static review found no blocking issues in the focused fix and regression test; runtime tests were not executed.

No open issues 🎉

What changed in this PR

Fixes room geometry import so physical groups spanning multiple surfaces contribute all their walls.

Changes:

• Collects mesh face nodes from every surface in each physical group instead of only the first.
• Adds a regression test verifying that merging surfaces into one physical group preserves the wall count.

File	Description
pyroomacoustics_method/​tests/​test_pyroomacoustics_backend.py	Adds wall-count regression coverage for multi-surface groups.
pyroomacoustics_method/​pyroomacoustics_interface/​pyroomacoustics_interface.py	Imports face nodes from all surfaces within each physical group.

_{Review effort: Balanced}